Conventional technology offers an image generation apparatus that performs high-speed rendering of objects such as polygon models by using Z-buffering. Z-buffering is one method for hidden surface removal (or in other words, visible surface determination). When Z-buffering is performed, a comparison of depths is performed between a depth of an already-rendered object and a depth of a rendering-target object, and when certain results are yielded through the comparison, rendering of the rendering-target object is not performed. Here, according to Z-buffering, values indicating depths of already-rendered objects are stored to a memory region as “Z depth values”. Further, the memory region to which such Z depth values are stored is commonly referred to as a “Z buffer”.
One problem with Z-buffering is that, when Z-buffering is performed, much access is made to the Z buffer. Hence, methods are sought for which reduce access made to the Z buffer.
For instance, Patent Literature 1 discloses one method for reducing access made to the Z buffer. In specific, Patent Literature 1 discloses a method where high order bits and low order bits of a Z depth value, which is stored to the Z buffer according to conventional technology, are separately stored to different memory regions. Further, according to the method disclosed in Patent Literature 1, a comparison of depths by using low order bits of the Z depth values is performed only when the determination of visible surface cannot be successfully performed by comparing high order bits of the Z depth values, or that is, only when a comparison of the Z depth values by using high order bits of the Z depth values cannot be successfully performed. According to this method, access is mainly restricted to that made to the memory region storing the high order bits of Z depth values, and accordingly, access made to the Z buffer is reduced. Note that in the following, a state where access is mainly made to only a specific memory region as described above is also referred to as the “localization of memory access”.